An in-vehicle system provided to a car is taken as an example. In the in-vehicle system, plural ECUs (Electronic Control Units) are each connected with a network, and I/O (I/O: INPUT/OUTPUT) devices for communicating with one of the plural ECUs are connected through a dedicated signal line. The one of the ECUs controls the I/O devices. In such an in-vehicle system, there has been a problem that as the number of I/O devices to be controlled increases, the number of dedicated signal lines connected to an ECU increases.
In order to solve the problem, Patent Document 1 discloses a method in which dedicated signal lines for the respective I/O devices are accommodated in any one of multiplex transmission devices installed in various portions of the vehicle, and the multiplex transmission devices are connected therebetween and to the ECUs, through multiplex transmission lines. However, in a case where plural ECUs are connected, the multiplex transmission lines are used not only for connecting a single ECU and the multiplex transmission devices, but also for connecting other plural ECUs to exchange data between ECUs and the like. Furthermore, because the data exchanged between the ECUs is utilized for controlling a moving car, a predetermined level of real time performance is required.
Furthermore, Patent Document 2 discloses a method in which in a communication system between a master station and plural slave stations (corresponding to the multiplex transmission devices), the plural slave stations are divided into groups according to their communication cycles, and the master station transmits a frame specifying a group to handle, to thereby communicate only with the specified group.